U.S. Pat. No. 4,420,754 discloses a system for measuring the relative movement between two elements, such as the scale and slide of a hand-held measuring instrument. The system includes the provision of a number of groups of supply electrodes on the slide, each of the electrodes in each group being supplied from a respective one of a multiple number of output signals from a signal generator so that all of the supply electrodes are furnished with voltages according to a cyclic pattern, the slide also having at least one receiving electrode which feeds a signal processing unit. The scale is provided with an electronic pattern comprising internally galvanically connected parts, one being a detecting part, located close to the area where the supply electrodes of the slide are moved, the other of the two parts being a transferring part which is located close to the area where the receiving electrode of the slide is moved. The movement of the slide along the scale generates a signal from the receiving electrode which is derived from the signals from at least two adjacent supply electrodes and the position of the slide is determined by a signal processing unit which identifies the amplitude ratio of the received signals.
U.S. Pat. No. 6,329,813 discloses an inductive absolute position sensor applying at least one magnetic field generator that generates a first changing magnetic flux in a first flux region. A plurality of coupling loops have a first plurality of coupling loop portions spaced at an interval related to a first wavelength along a measuring axis and a second plurality of coupling loop portions spaced at an interval related to a second wavelength along a measuring axis. One of the first plurality of coupling loop portions and the second plurality of coupling loop portions are inductively coupled to a first changing magnetic flux from a transmitter winding in a first flux region to generate a second changing magnetic flux outside the first flux region in the other of the first plurality of coupling loop portions and the second plurality of coupling loop portions. A magnetic flux sensor is positioned outside the first flux region and is responsive to the second changing magnetic flux to generate a position-dependent output signal. The output signal varies at the first or second wavelength of the corresponding other of the first plurality of coupling loop portions and the second plurality of coupling loop portions that generates the second changing magnetic flux.
The arrangements suggested in both U.S. Pat. Nos. 4,420,754 and 6,329,813 are adapted for determining linear translations between two objects.
US 2004/0207385 relates to a device for contact free detection of a position of a rotor relative to a stator, where at least one electrode is arranged on the rotor and at least one electrode is arranged on the stator. The electrodes overlap in at least one rotational position of the rotor relative to the stator. US 2004/0207385 further relates to a corresponding method for measuring the rotational position of a rotor relative to a stator. The rotational position is detected using a capacitive coupling between the rotor electrode and the stator electrode.
US 2004/0207385 relates to contact free determination of angular positions between two objects such as between a rotatably mounted rotor and a stationary stator. It is a disadvantage of the arrangement suggested in US 2004/0207385 that the emitters and receivers are position in a manner where they take up an unnecessary amount of space. For compact systems the solution suggested by US 2004/0207385 is not applicable.
WO 02/092153 relates to a medication injector apparatus with various arrangements for position determination. The arrangement depicted in FIG. 20 of WO 02/092153 is constituted by an electrically conducting matrix where six horizontally oriented rows are connected by vertically oriented matrix elements. The six horizontally oriented rows and the vertically oriented matrix elements constitute an integrated electrically conducting matrix.
U.S. Pat. No. 5,986,585 relates to a device for converting mechanical deflections into corresponding electrical variables. Two pairs of contact terminals are moveably arranged relative to two groups of contact pads where driving signals are provided to one of said groups. One or more output signals are retrieved from one or more electrodes of the second group—said one or more output signals being indicative of the position of the contact terminals relative to the two groups of contact pads. The arrangement suggested in U.S. Pat. No. 5,986,585 is not suitable for measuring angular positions between two elements.
It is an object of the present invention to provide a space saving arrangement for measuring absolute position of a first member, such as a dose indicator barrel, relative to a second member, such as a housing of a medication delivery device.